L-FABP AND I-FABP EXPRESSION INCREASE NBD-STEARATE UPTAKE AND CYTOPLASMIC DIFFUSION IN L-CELLS

The effects of intestinal and liver fatty acid binding protein (I- and L-FABP, respectively) expression on single-cell fatty acid uptake, in ternalization, and cytoplasmic diffusion were determined in transfecte d L cell fibroblasts. These parameters were measured using the noneste rifiable fluorescent fatty acid probe methyl-(7-nitrobenz-2-oxa-1,3-di azol)aminostearate (NBD-stearate) and fluorescence digital imaging. In single-cell fluorescence imaging experiments, L-FABP-expressing cells , but not I-FABP-expressing cells, increased NBD-stearate uptake 1.7-f old compared with control cells. Both I- and L-FABP increased the cyto plasmic diffusion rate of the internalized NBD-stearate 2.6- and 1.9-f old, respectively, compared with control cells. However, increased NBD -stearate lateral membrane mobility was observed only in L-FABP-expres sing cells. After incubation of the cells with 4 mu M NBD-stearate at 37 degrees C for 30 min, fluorescence deconvolution imaging indicated that NBD-stearate was localized primarily into lipid droplets in all c ell lines. The differential effect of these proteins on fatty acid upt ake and intracellular trafficking in single cells illustrates a possib le difference in the physiological function of I- and L-FABP in intact cells.